PMD is disease of peripheral corneal thinning that is slowly progressive over many years. It is becoming increasingly important to recognize as it can cause severe deterioration in visual function. Also, patients who undergo refractive surgery with PMD can have deleterious results, so it is important to consider prior to refractive surgery.
PMD, while rare, is the second most common noninflammatory corneal thinning disorder behind keratoconus. Some people postulate, however, that this prevalence might be underestimated as the condition is often misdiagnosed as keratoconus. Keratoconus, keratoglobus, and PMD are postulated to be related because these conditions coexist in families. Ten percent of PMD cases are associated with keratoconus and 13% are associated with keratoglobus. In Japan, 17 of 20 cases of PMD occurred ipsilaterally with keratoconus in the eye. It has not been elucidated whether keratoconus, keratoglobus, and PMD are different diseases or phenotypic variations of the same disease.
PMD typically presents in the second to fifth decade of life. PMD has no sex or racial predilection, and does not appear to be hereditary, but moderate to high astigmatism has been noted in families with affected patients. A recent case showed that PMD was coexistent with corneal plana in an individual with a KERA mutation, thus, potentially implicating keratocan in the development of PMD.
Because of extremely abnormal corneal topography, the treatment of PMD is difficult. Therapeutic options are limited by the degree of corneal protrusion. A recent study at a tertiary care center found that 88% of PMD cases were managed nonsurgically with spectacles (36%) or contacts (52%), whereas 12% underwent penetrating keratoplasty.